Lecture 21 –Alternative Lithography Techniques

EECS 598-002 Winter 2006Nanophotonics and Nano-scale Fabrication

P.C.Ku

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Overview

Immersion lithographyEUV lithographyInterference lithographyImprint lithographyMaskless lithography (ML2)

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Trends in lithography

Resolution limit = k1λ/NA and NA = nsinθ

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Immersion lithography

Resolution limit = λ/2NA and NA = nsinθConventional lithography: n = 1Immersion lithography: n = 1.44 (pure water)

Current projected limit = 35 nm half pitch.

Issues need to be taken care of:Possible bubbling of waterWater temperature control to keep the refractive index constantWater-resist interaction resist needs to be water resistantMetrology (e.g. registration) can be a challenge if done throughwater

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How to introduce water?

Swimming pool designEntire stage under water

Bathtub designEntire wafer under water

Shower designWater is injected to the part of the wafer that’s going to be exposed.

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Shower design

Wafer edgeexposuremay bean issue.

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First generation of immersion tools

NA < 1. But DOF is improved.

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Extreme UV lithography (EUVL)

At wavelength of 13-14 nm: no refractive optics. Need to use reflection optics. Reflectors are made of Mo/Si Bragg reflectors.

EUVL mask

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EUVL system schematic

From Nanoelectronics and Information Technology

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Interference lithography

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Extension from conventional lithography

-1-1

-2

-3

1

-4

-2

Add intensities from exposures with different illumination angles.Add in zero order through a separate optical path when needed.

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Why do we need the zero-th order

ConventionalExposure

High SpatialFrequencies Only

High SpatialFrequencies

Plus Zero Order

PrintedResist

CalculatedImage

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Implementation of IIL

Zero order light follows thepath on the right.

The movable mirror M1 selectsthe diffraction orders that willadd with zero order at the wafer.

The effective NA approachessin(U+sin-1NAobj).

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IIL with i-line lithography

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Multiple beam interference

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Imprint lithography

Nice tutorial on the web: link

http://www.molecularimprints.com/Technology/technology2.html

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Maskless lithography (ML2)

SCAPAL (scattering with angular limitation in projection electron beam lithography)

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Proximity effect in e-beam lithography

Resolution limit is not determined by electron wavelength but rather by backscattered electrons (proximity effect.)

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Schedule for the rest of the semester

EtchingThin film depositionSelf-assembly and hybrid nanofabricationMiscellaneous e.g. VLS nanowire growth, …Summary of the course and outlook

+ guest lecture on photonic crystals (time TBA)